Fluid drop marking apparatus

ABSTRACT

A fluid drop marking apparatus which generates a plurality of fluid marking streams from a set of orifices spaced apart along a closed contour in an orifice plate. The streams are stimulated to create a corresponding set of drop trains and the drops are selectively charged by application of an electrical signal to a conductive surface surrounding the streams at their breakup points. The conductive surface extends downstream for production of outwardly attractive images of the drop charges; thereby causing the charged drops to be deflected outwardly for selective catching by an apertured catching plate. Halftone representations are created by modulation of the applied electrical signal; the nature of the modulation depending upon the type of catching plate aperture employed.

United States Patent 1 1 3, 56,174 Robertson 1451 Apr. 11,1972

54] FLUID DROP MARKING APPARATUS 3,560,641 2/1971 Inventor: John A.Robertson, Chillicothe, Ohio Assignee'. The Mead Corporation, Dayton,Ohio Filed: Feb. 26, 1971 Appl. No.: 119,230

Related U.S. Application Data Field of Search ..346/l, 75, 140; 239/15,3; 209/127 R, 127 C, 3; 178/66; 317/3 References Cited UNITED STATESPATENTS 3/1968 Sweet et a1 346/75 12/1968 Hertz et a1. ..346/75 Tayloret a1 ..346/75 X Primary Examiner-Joseph W. Hartary Attorney-John W.Donahue [5 7] ABSTRACT A fluid drop marking apparatus which generates aplurality of fluid marking streams from a set of orifices spaced apartalong a closed contour in an orifice plate. The streams are stimulatedto create a corresponding set of drop trains and the drops areselectively charged by application of an electrical signal to aconductive surface surrounding the streams at their breakup points. Theconductive surface extends downstream for production of outwardlyattractive images of the drop charges; thereby causing the charged dropsto be deflected outwardly for selective catching by an aperturedcatching plate. Halftone representations are created by modulation ofthe applied electrical signal; the nature of the modulation dependingupon the type of catching plate aperture employed.

4 Claims, 5 Drawing Figures PATENTEUAPR 1 1 1912 SHEET 1 0F 2 INVENTOR.JOHN A. ROBERTSON ATTORNEY PATENTEDAPR 11 m2 3,656,174

SHEEI 2 [IF 2 INVENTOR. JOHN A. ROBERTSON BY M (l-0W ATTORNEY FLUID DROPMARKING APPARATUS CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OFTHE INVENTION This invention relates to the general field of fluid dropmarking and more particularly to fluid drop marking apparatus of thetype wherein a marking fluid is forced through an orifice under pressureand is stimulated upon exit therefrom to break up into a train ofuniformly sized and regularly spaced drops. Typical prior art devices ofthis type are shown in Lewis et al. US. Pat. No. 3,298,030 and in Sweetet al. U. S. Pat. No. 3,373,437. Such devices ordinarily employ acharging electrode for capacitive charging of the drops duringformation. Thereafter they variably deflect the drops by subjecting themto the action of a steady state electrical field.

Certain of the drops which are charged to deflect more than somepredetermined distance are ordinarily caught. The catcher for such apurpose may be a porous block as shown in the mentioned Sweet et al.patent, a simple funnel as shown in the mentioned Lewis et al. patent,or an apertured plate as shown for instance in Hertz et al. US. Pat. No.3,416,153 or Nordin U.S. Pat. No. 3,500,436.

As disclosed in the parent patent application, it is possible toeliminate the requirement for a steady state electrical deflection fieldby providing a laterally non symmetrical conductive surface to enabledrop deflection by a self induced electrical field. In general it is anobject of the present invention to provide an apparatus using theprinciples of the invention of the parent application and which isparticularly well adapted for halftone recording of graphic information.

It is another object of the invention to provide a jet drop recordingapparatus of reduced complexity.

Another object of the invention is to provide a fluid drop markingapparatus having improved marking accuracy.

Still another object of the invention is to provide apparatus fordigital jet drop recording at increased information rates and withrelatively small sized drops.

Additional objects and features of the invention will become apparent byreference to the following description together with the accompanyingdrawings and claims.

SUMMARY OF THE INVENTION This invention accomplishes the aforementionedobjects by creating a plurality of trains of uniformly sized andregularly spaced drops, directing these drops through an aperture in acatching plate, and selectively deflecting drops outwardly beyond theaperture lip by employment of self induced deflection fields. The dropstrains are created by forcing a marking fluid through a plate andapplying a constant frequency drop stimulating disturbance to theresulting set of issuing fluid streams. As the drops are generated theyare selectively charged by controlled application of a capacitivecharging voltage between the fluid streams and a surrounding conductivesurface. Thereafter the drops are deflected outwardly by the attractiveaction of self-induced image charges in a downwardly extending portionof the conductive surface. Halftone representations may be created byemploying a non coincident catching plate aperture and modulating theamplitude of the drop charging voltage for catching of a predeterminedpercentage of the drops generated during any given stimulation cycle.Alternatively, halftone representations may be created by employing acoincident catcher together with on/off modulation of the drop chargingvoltage in accordance with an appropriately timed schedule.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cut awayrepresentation of a general apparatus arrangement constructed inaccordance with this invention.

FIG. 2 is a cut away schematic representation of one species of theinvention.

FIG. 3 is a diagrammatic illustration of the distribution of actual andimage charges induced in a conductive wall by the presence of a nearbycharged drop.

FIG. 4 is an illustration of a catching plate aperture for use ingenerating halftone representations.

FIG. 4a illustrates a charging voltage sequence for use in connectionwith the catching plate aperture of FIG. 4 to produce 5 halftonedensities ranging from black to white.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred arrangement forthis invention is shown generally in FIG. 1 wherein are illustrated aset of circularly disposed fluid filaments 1 issuing from a set oforifices 2 in an orifice plate 3 and breaking up into drops 5.Surrounding filaments 1 is a conductive cylindrical tube 4 which isadapted for capacitive charging and self induced outward deflection ofdrops 5. Drops 5 accordingly (but only if charged) fall beyond theupstanding lip 6 of apertured catching plate 7 and are caught. They arethen drawn away by a vacuum (not illustrated).

FIG. 2 illustrates the above mentioned drop marking operation insomewhat more detail for only two streams. As shown in FIG. 2 a fluidsupply chamber 8 having upper and lower sections 9 and 10 contains asupply of marking fluid 11. Fluid 11 is supplied to chamber 8 by conduit23 and is maintained under pressure by any convenient means such as apump 22. A filter screen 12 removes any large particulate matter fromfluid 11 thereby preventing any plugging of orifices 2. A stimulationtransducer 13 transmits constant frequency vibrations through thestructure of chamber 8 to filaments 1 thereby causing regularly timedformation of uniformly sized drops. The drop stimulation process is wellknown in the prior art, and a variety of stimulation transducers areavailable. Accordingly transducer 13 may be magnetostrictively driven ormay be replaced by a piezoelectric device which may be bonded directlyto chamber 8 or to orifice plate 3. The vibration frequency should besomewhere near the natural frequency of streams l which in onesuccessfully operated embodiment is about kHz. Associated with thisfrequency area fluid pressure of,2.l kg. per sq. cm. and an orificediameter of 1 1.4 microns. The apparatus conveniently employs sixorifices on a 204 micron diameter circle. The stimulation frequencyshould be increased with increasing fluid pressure or with a decreasedorifice diameter.

Drops 5 may be selectively charged by applying a charging signal 26 tothe input terminals 24 of an amplifier 14. The output terminals ofamplifier 14 are connected to orifice plate 3 and to tube 4. This setsup an electrical field between the conductive inner surface of tube 4and the outer surface of filaments 1. As a result, filaments 1 arecapacitively charged and this charge is carried away by drops 5. Thistechnique for drop charging is generally the same as that employed inthe prior art as shown for instance in Lewis et al. US. Pat. No.3,298,030. However, in contrast to prior art charging electrodes,conductive tube 4 extends relatively far below the drop breakoff pointsthereby providing an imaging surface for self induced deflection of thecharged drops. For the above mentioned sixorifice configuration, tube 4may be about 380 microns in dia. and extend about 1,800 microns belowthe drop formation point. The charging potential may be about 200 volts.

The drop deflection phenomenon may be understood by referring to FIG. 3wherein a charged drop 15 is shown falling past a conductive wall 16.Drop 15 carries distributed negative charges 17 which induce charges 18on the surface of wall 16. Charges l8 attract drop 15 toward wall 16with a cumulative effect equivalent to that of a hypothetical image drop20 carrying image charges 21. Lines 19 represent the total electricalfield between drop 15 and wall 16. The force acting on drop 15 is givenapproximately by the equation 3 where Q is the total charge on drop 15,s is the permittivity of air and d is the distance from drop to thesurface of wall 16.

It should be apparent that a second wall placed opposite wall 16 on theother side of drop 15 would set up attractive forces cancelling theeffect of wall 16. This same cancelling effect is present when a singletrain of charged drops passes down the axis of a cylindrical conductivesurface. Thus, as explained in more detail in the parent application, itis necessary that the conductive surface have a laterallynon-symmetrical configuration with respect to the initial droptrajectory. This condition necessarily obtains when the conductivesurface is cylindrical and surrounds a plurality of drop trains, all ofwhich are offset from the cylinder axis.

Referring again to FIG. 2, there are illustrated a set of drops 5a whichare not caught but have passed through the aperture in catching plate 7for deposition on the moving recording medium 25. Drops 50 were allformed when signal 26 was at the zero level. These drops received noelectrical charge and fell through tube 4 without deflection; thesubsequent change in tube potential having no effect upon theirtrajectories. Drops 5 on the other hand were all formed after signal 26jumped from a zero to a non zero magnitude and accordingly have beenoutwardly deflected for catching. Thus the apparatus produces a recordedline which corresponds to on/off states in the input control signal.

It should be appreciated that the above described apparatus will print 6circularly arranged dots on recording medium during one stimulationperiod. The individual dots typically will have a diameter of about 40microns whereas the circle of dot centers will have a diameter of 204microns. Thus to achieve solid coverage it becomes necessary to adjustthe movement speed of recording medium 25 so as to allow time fordeposition of several overlapping dot sets while the recording mediummoves for a distance of 204 microns. A halftone gray scale may becreated by merely charging and catching various ones of theseoverlapping dot sets. The large 204 micron circle thus may be consideredthe basic system resolution cell corresponding to one square in ahalftone screen. Techniques well known in communication theory may beapplied to achieve modulation of the charging voltage signal appropriatefor creation of the above described halftones.

Another method of generating halftone representation with the apparatusof this invention makes use of a non coincident catching plate aperture.FIG. 4 illustrates such an aperture which may be used in combinationwith a set of four drop trains. In general such a non coincidentaperture may have a contour which is shaped differently from the contourpassing through the centers of the orifice plate orifices, or else itmay be similarly shaped and merely laterally offset whereby an equaloutward deflection of all drop trains results in catching of the dropsin one or more trains with passage through the aperture of the drops inthe other trains. For comparison note the coincident circular catchershown in FIG. 1 in combination with a circular array of orifices. Alldrops generated by such an arrangement during one stimulation period aresimilarly charged and deflect outwardly in a conical manner with a conehalf-angle dependent upon the level of the charging voltage. Catchingplate 7 catches all drops in one six-drop cluster, (i.e., six circularlydisposed drops generated from fluid filaments 1 during a singlestimulation period) or else it catches none of them. It cannotselectively catch only certain drops within a single cluster.

In contrast thereto, aperture 27 when used non coincidently with 4equally spaced drop trains as shown in FIG. 4 may print five differentdensity levels ranging from black to white. FIG. 4 illustrates fivesequential catching plane positions which the four mentioned drop trainsmay reach when the four parent field filaments have been sequentiallycharged by five voltage levels as shown in FIG. 4a.

Drop positions A represent the lateral location at the catching plateplane for drops beingformed when the charging signal is at level a. Iflevel a has a magnitude of zero volts, then the spacing betweenpositions A is identical to the spacing of 4 corresponding orifices inthe orifice plate.

When the charging signal is raised to lever b the drops then beingformed are slightly charged and accordingly are deflected outwardly ashort distance. Drops from 3 of the drop trains pass through position Band eventually will reach the recording medium. However drops in thefourth train are deflected to position B which is beyond the edge ofaperture 27 and accordingly are caught. Thus when the charging signal israised from level a to level b, the amount of marking fluid reaching therecording medium is decreased by 25 percent. Similarly when the chargingsignal is raised to level c two drop trains are deflected to passthrough two non catching positions C while the other two drop trains aredeflected to two catching positions C. This reduces the quantity ofdeposited marking fluid by a total of 50 percent.

Continuing as above, the charging signal may be raised to levels d and efor drop deflection to positions DD and E,E'. The drop catchingpositions are in all cases illustrated in a striped fashion while thepassage or non catching positions are solid. It is therefore seen how anon coincident four sided catcher may be used in combination with fourdrop trains and five charging signal levels to produce five markingintensity levels ranging from black to white. The invention mayobviously be extended to produce additional halftone levels by addingadditional streams, charging levels and aperture sides.

What is claimed is:

1. Fluid drop marking apparatus comprising:

1. an orifice plate provided with a plurality of orifices spaced apartalong a closed contour,

2. a marking fluid supply reservoir communicating with said orifices,

3. means for applying pressure to marking fluid within said reservoirand causing streams of marking fluid to be projected from the orifices,

4. means for stimulating said streams and causing them to break up intotrains of uniformly sized and regularly spaced drops,

5. a closed contour electrically conductive surface surrounding thestreams at their breakup points and connected to a source of variableelectric potential for capacitive inducement of predetermined electricalcharges in selected drops; said surface extending downwardly from saidbreakup points for production of outwardly attractive images of saidcharges, and

6. an apertured catching plate positioned for passage of said droptrains through the aperture thereof; said aperture being contoured forcatching of drops deflected therebeyond by the attractive action of saidimages.

2. Apparatus according to claim 1 the orifices in said orifice platebeing circularly arranged and the aperture in said apertured catchingplate being of circular configuration and in line with the circularlyarranged orifices for operation as a coincident catcher.

3. Apparatus according to claim 1, the aperture in said aperturedcatching plate being non coincident for production of halftonerepresentations.

4. Fluid drop marking apparatus comprising:

1. an orifice plate provided with a plurality of orifices spaced apartalong a closed contour,

2. a marking fluid supply reservoir communicating with said orifices,

3. means for applying pressure to marking fluid within said reservoirand causing streams of marking fluid to be projected from the orifices,

4. means for stimulating said streams and causing them to break up intotrains 1 of uniformly sized and regularly spaced drops,

5. means for inducing predetermined electrical charges in selected dropsand producing outwardly attractive images of said charges, and

6. an apertured catching plate positioned for passage of said droptrains through the aperture thereof; said aperture being non coincidentfor production of halftone representations by selective catching ofdrops deflected therebeyond by the attractive action of said images.

1. Fluid drop marking apparatus comprising:
 1. an orifice plate providedwith a plurality of orifices spaced apart along a closed contour,
 2. amarking fluid supply reservoir communicating with said orifices, 3.means for applying pressure to marking fluid within said reservoir andcausing streams of marking fluid to be projected from the orifices, 4.means for stimulating said streams and causing them to break up intotrains of uniformly sized and regularly spaced drops,
 5. a closedcontour electrically conductive surface surrounding the streams at theirbreakup points and connected to a source of variabLe electric potentialfor capacitive inducement of predetermined electrical charges inselected drops; said surface extending downwardly from said breakuppoints for production of outwardly attractive images of said charges,and
 6. an apertured catching plate positioned for passage of said droptrains through the aperture thereof; said aperture being contoured forcatching of drops deflected therebeyond by the attractive action of saidimages.
 2. a marking fluid supply reservoir communicating with saidorifices,
 2. a marking fluid supply reservoir communicating with saidorifices,
 2. Apparatus according to claim 1 the orifices in said orificeplate being circularly arranged and the aperture in said aperturedcatching plate being of circular configuration and in line with thecircularly arranged orifices for operation as a coincident catcher. 3.Apparatus according to claim 1, the aperture in said apertured catchingplate being non coincident for production of halftone representations.3. means for applying pressure to marking fluid within said reservoirand causing streams of marking fluid to be projected from the orifices,3. means for applying pressure to marking fluid within said reservoirand causing streams of marking fluid to be projected from the orifices,4. means for stimulating said streams and causing them to break up intotrains of uniformly sized and regularly spaced drops,
 4. means forstimulating said streams and causing them to break up into trains ofuniformly sized and regularly spaced drops,
 4. Fluid drop markingapparatus comprising:
 5. means for inducing predetermined electricalcharges in selected drops and producing outwardly attractive images ofsaid charges, and
 5. a closed contour electrically conductive surfacesurrounding the streams at their breakup points and connected to asource of variabLe electric potential for capacitive inducement ofpredetermined electrical charges in selected drops; said surfaceextending downwardly from said breakup points for production ofoutwardly attractive images of said charges, and
 6. an aperturedcatching plate positioned for passage of said drop trains through theaperture thereof; said aperture being contoured for catching of dropsdeflected therebeyond by the attractive action of said images.
 6. anapertured catching plate positioned for passage of said drop trainsthrough the aperture thereof; said aperture being non coincident forproduction of halftone representations by selective catching of dropsdeflected therebeyond by the attractive action of said images.